1. Field of the Invention
The invention relates to an injection system for feeding a particulate material to a process vessel, which in a particular embodiment could include, for example, feeding consistent amounts of catalyst to a polyethylene reactor over an extended period of time.
2. Description of the Prior Art
Various systems have been proposed that provide catalysts or other particulates to a reactor, such as a polyethylene reactor, in measured quantities over an extended period of time. Such systems have included various combinations of valves and have utilized pressurized feed gas or sweep streams of inert gases to mobilize, or transport, the particulate from a particulate storage vessel to the reactor. Some systems repeatedly open and close a particulate feed valve to allow measured doses of the particulate to flow from the particulate storage vessel aided only by gravity directly to the reactor, or they may utilize an intermediate chamber in which to deposit the measured doses of particulate prior to flushing the particulate from the intermediate chamber by use of a feed gas or sweep stream. However, such prior systems have failed to adequately provide an efficient method of accurately and consistently providing the measured dose of particulate to the reactor.
Various valve designs have been utilize to improve the accuracy of the particulate dosage. For example, rotary valves have been utilized by replacing standard cylindrical or spherical rotors in rotary valve devices with modified rotors having a cup-shaped cavity formed therein for receiving the measured particulate dose. The rotor can then be rotated, or inverted, between a first, or filling, position for filling the cavity with particulate from the particulate storage vessel and a second, or releasing, position for releasing the particulate into the intermediate chamber. Such prior rotary valve devices may produce less than exact measured doses to the reactor because amounts of the particulates may remain inside the cup-shaped cavity after being rotated into the second, or releasing, position. Prior systems have attempted to minimize this problem and have included small ball bearings, or "chatter plates", into the bottom of the cavity, which are intended to mechanically clear any remaining particulates from the bottom of the cavity when rotated or inverted to the releasing position. Prior systems have proved to be costly, complicated, and difficult to maintain.
Prior systems have proved to be inadequate for providing precise, measured, doses of particulates to reactors over extended periods of time, and have proved to be complicated and difficult to maintain. Accordingly, prior to the development of the injection system of the present invention, there has been no injection system for feeding particulate to a reactor that provides efficient and consistent dosages of particulates to a reactor over an extended period of time, and which are simple, inexpensive to maintain, have very few moving parts, and minimize failure. Therefore, the art has sought an injection system for feeding particulate to a reactor that provides efficient and consistent dosages of particulates to a reactor over an extended period of time, and which are simple, inexpensive to maintain, have very few moving parts, and minimize failure.
Furthermore, the art has sought a means for eliminating concentrated clumps or "slugs" of particulate which when the particulate is a catalyst tend to result in local areas of high activity in the reactor and subsequent fouling.